The present invention pertains to a high-purity Ru alloy target for sputtering having a purity of 3N (99.9%) or higher and which is suitable in forming a capacitor electrode material of a semiconductor memory, a manufacturing method of the foregoing Ru alloy target, and a high-purity Ru alloy sputtered film obtained by sputtering this Ru alloy target.
Today, the use of Ru as an electrode material or the like of a semiconductor capacitor is rapidly expanding. This kind of electrode is generally formed by sputtering a Ru target.
In order to guarantee the operational performance as a reliable semiconductor, it is important to reduce as much as possible impurities in the foregoing materials formed after sputtering that are harmful to the semiconductor device. In other words, it is desirable to reduce the following impurities as much as possible, and realize a purity of 3N or higher, namely 99.9% (weight) or higher:
alkali metal elements such as Na and K;
radioactive elements such as U and Th; and
transition metal elements such as Fe, Ni, Co, Cr and Cu.
The reason the foregoing impurities are harmful is that alkali metals such as Na and K move easily in the gate insulator and cause the MOS-LSI interfacial quality to deteriorate, radioactive elements such as U and Th cause a soft error of elements due to the α rays emitted from such elements, and transition metal elements such as Fe, Ni, Co, Cr and Cu contained as impurities cause trouble at the interface bonding.
Among the above, the harmful effect of alkali metals such as Na and K is particularly pointed out.
Although a target is generally prepared by the powder sintering method, an Ru target based on a conventional powder sintering method entails numerous problems such as high-impurity concentration; particularly, high concentration of alkali metals such as Na and Ka, which leads to the deterioration in characteristics of high-integrated semiconductors, and high concentration of gas components such as C and O, which leads to the generation of numerous particles during sputtering deposition.
In order to overcome the foregoing problems of a Ru target prepared by the powder sintering method, preparation of a target by the dissolution method is being considered. Nevertheless, since the Ru target prepared by the dissolution method has large crystal grains, the sputtering ratio will differ depending on the crystal face, and there is problem in that the film thickness distribution of the Ru sputtered film will become uneven.
As manufacturing technology of conventional dissolution methods, there are the following. A sputtering target comprising Si at 1 to 9 ppm and Ru as remnants at 99.998% or higher, and powder for manufacturing such a sputtering target (Patent Document 1); a molten target comprising Ru having a purity level of 99.998% or higher, wherein the oxygen contained in this molten target is 0.1 to 20 ppm (Patent Document 2); a ruthenium sputtering target obtained by plasma-arc melting or arc melting, wherein hydrogen is 5 ppm or less, and tungsten or tantalum is 5 ppm or less (Patent Document 3); and a sputtering target obtained by cutting the top and bottom faces of a ruthenium ingot having a purity level of 3N or higher obtained by the dissolution method, and performing compression forming to the cut ingot at a prescribed temperature and surface pressure (Patent Document 4).
Nevertheless, as a sputtering target material to be used in forming a capacitor electrode material of a semiconductor memory, characteristics where the generation of particles during deposition is minimal and the film thickness distribution is uniform are required, but there is a problem in that such characteristics of the foregoing Patent Documents are insufficient under the existing circumstances.
[Patent Document 1]
    Japanese Patent Laid-Open Publication No. 2000-178721[Patent Document 2]    Japanese Patent Laid-Open Publication No. 2000-178722[Patent Document 3]    Japanese Patent Laid-Open Publication No. 2003-277924[Patent Document 4]    Japanese Patent Laid-Open Publication No. 2004-156114